When 16.8 g of a white solid X was heated 4.4 g of an acid gas A which turned lime waer milky, was driven off together with 1.8 g of a gas B which condensed to a colourless liquid. The solid that remained Y dissolved in water to give an alkaline solution which with excess barium chloride solution gave a white precipitate Z. The precipitate effervesced with acid giving carbon dioxide. Identifu A,B and Y and write the quation for the thermal decomposition of X.

Explanation

`X:NaHCO_(3)` `Y:Na_(2)CO_(3)`
`A:CO_(2)` `B:H_(2)O`
`2MHCO_(3)overset(Delta)toM_(2)CO_(3)+CO_(2)+H_(2)O`
The gas A is carbon dioxide coming form a bicarbonate along with water B.
If 4.4. g `CO_(2)` comes from 16.8 g of salt, then 44 g (1 mol) `CO_(2)` must come from
`(16.8)/(4.4)xx44=168 g` of salt.
So the molecular mass of the salt is
`(168)/(2)=84`
According M should be sodium
`2NaHCO_(3)overset(Delta)toNa_(2)CO_(3)+CO_(2)+H_(2)O`
`CO_(2)+Ca(OH)_(2)toCaCO_(3)darr+H_(2)O`
`Na_(2)CO_(3)+BaCl_(2)toBaCO_(3)darr+NaCl`
`BaCO_(3)+2"HCl"toBaCl_(2)+H_(2)O+CO_(2)`